It is known to increase power output and torque from combustion engines by using “tuned” intake systems. Such intake systems use the inertia of air that is about to get inducted by the engine in order to increase the volumetric efficiency of the engine, i.e., the amount of air that is inducted in to the engine cylinders for each engine cycle. One drawback with tuned exhaust systems is however that the tuning effect is limited to a rather narrow engine speed range; more efficient tuning leads to an even narrower engine speed range with working tuning. Moreover, tuning of an engine in a specific speed range actually lowers the engines volumetric efficiency outside this speed range.
In a tuned intake system, the intake valves induct air through a “pipe”. As is well known by persons skilled in the art, a suction wave that meets a thinner medium is reflected as a pressure wave (and vice versa, a pressure wave is reflected as a suction wave). A thinner medium is in this context a pipe with a larger diameter. As also is well known by people skilled in the art, induction of air into the cylinder results in a suction wave; as this suction wave meets a thinner medium, i.e. a diameter increase at the end of the pipe, it will be reflected as a pressure wave. In a properly tuned intake system, the pressure wave should reach the intake valves just before they close, and in that way press in an extra amount of air into the cylinder. As can be understood, and as stated above, this type of tuning only works in a narrow engine speed range; if the engine speed is too high, the pressure wave will not reach the intake valve in time; if it is too low, the extra air that is pressed into the cylinder by the pressure wave will have time to escape back through the open intake valves. As mentioned, one problem with tuned intake systems is that they actually decrease the engines volumetric efficiency outside the specified engine speed range, which will render the engine torque as a function of engine speed uneven. The more efficient the tuning, the narrower the tuned engine speed range, and the worse the engines volumetric efficiency will be outside the tuned speed range.
In order to avoid the above problems, variable intake systems have been developed. On such intake systems, it is possible to vary the effective length of the intake pipe. This is mostly done by a valve that punctures the intake “pipe” in order to shorten the effective length, i.e. the length from the intake valve of the engine to the thinner medium. Such systems are well known by persons skilled in the art, and function well to give engines smooth running characteristics over a wide engine speed range.
Inventors herein have recognized a problem concerning the combination of variable intake systems and engines comprising electronically controlled fuel injection systems; such fuel injection systems rely on a “fuelling map” that controls the amount of injected fuel based on information on intake manifold pressure, engine speed and the volumetric efficiency of the engine. If the volumetric efficiency of the engine is not what is expected in the fuelling map, an emission increase will result. This is due to the effect that valve degradation may affect the amount of air inducted to the engine, compared to what would be the case if the valve would function properly; this “fools” the engine controller to inject an amount of fuel that either leads to a too “lean” or to a too “rich” combustion (lean and rich combustion is engine jargon for air/fuel mixtures that contain too small or too large amounts of fuel, compared to the amount of air that is needed for a complete combustion).
For steady state conditions, the amount of injected fuel is “fine-tuned” by information from an oxygen sensor in the exhaust system, but for transient load conditions, there will be an emission increase (steady state means that the engine runs on the same speed and load for an extended period of time—transient means that the engines speed and/or load changes).
Therefore, it is important to diagnose degradation in such systems, and to minimize emissions increase due to the degradation.
U.S. Pat. No. 5,138,874 describes a diagnosis system for an engine comprising an intake system with reed valves. The diagnosis system comprises a pressure sensor placed in the intake system, which pressure sensor is connected to an engine controller. The engine controller takes samples of the pressure in the intake system as a function of crank angle degree, (CAD); if the pressure fluctuations, i.e. the pressure variations, would exceed a certain value, the engine controller is informed that any of the reed valves is defect. As a reaction to the information, the ECU informs the driver about the reed valve degradation.
However, U.S. Pat. No. 5,138,874 does not describe a reliable method for calculating the pressure fluctuation level without taking samples of the pressure as a function of CAD. This is probably due to the fact that a failing reed valve gives so large pressure fluctuation that a more sophisticated calculation method is not needed. For more normal intake systems, i.e., intake systems without reed valves, the method according to U.S. Pat. No. 5,138,874 is not sufficient.
Another drawback with the invention described in U.S. Pat. No. 5,138,874 is that the method described therein requires a lot of processor power; taking pressure samples as a function of CAD means much more work for the processor comprised in the engine controller, ECU.
Moreover, U.S. Pat. No. 5,138,874 fails to describe how to minimize emissions in case of a reed valve degradation.
The present invention is aimed to solve the problem with the increased emissions that results from degraded intake system. The invention also aims to solve the problem with diagnosis of intake system degradation, without increasing the demands on processor capacity in the engine controller, ECU, unnecessarily much.
The above problems are solved by an internal combustion engine, wherein an engine controller adapts a fuelling map responsive to diagnosis of degradation of at least one valve of the variable intake system.
It is beneficial if a pressure sensor is placed in an intake plenum feeding one cylinder bank in an engine of V-configuration, since tests have shown that this position gives a large pressure variation difference.
Further, it is beneficial if the variable intake system comprises two separate intake plenums which are separated by a partitioning wall, that merges into a secondary pipe and are interconnected by at least one butterfly valve.
It is also beneficial if a pressure sensor is placed in either of the intake plenums, since it is unnecessary to use more than one pressure sensor.
The above advantages and other advantages, and features of the present invention will be readily apparent from the following detailed description of the preferred embodiments when taken in connection with the accompanying drawings, and from the claims.